Commercial preparation of condensation polymers such as polyesters and polyamides is characteristically accomplished by a process known as polycondensation performed in a reactor vessel wherein some form of agitator is used to induce evaporative release of a volatile constituent material in the polymer being processed. In this manner, the viscosity of the polymer and the viscous uniformity thereof may be selectively increased.
In a conventional vessel of the aforedescribed type, this polycondensation process is carried out continuously by introducing the low viscosity polymer at one end of the vessel and conveying it through the vessel to an outlet adjacent the opposite end of the vessel, while subjecting the polymer to the action of the agitator during the period of residence of the polymer within the vessel. The vessel is oriented on a horizontal axis and the agitator is characteristically in the form of a coaxially rotated cage having perforated or otherwise screen-like elements mounted radially to a central drive shaft to be progressively coated with the polymer and also having peripheral wiping elements to progressively apply a film-like coating of the polymer to the annular interior wall of the vessel, the combined action of the screens and wiping elements serving to increase the exposed evaporative surface of the polymer as the agitator progressively rotates. Such apparatus are commonly referred to in the trade as "wiped wall" polymer reactors, one representative example of such a reactor being disclosed in U.S. Pat. No. 3,248,180.
As polymer technology has advanced and industry has continued to demand polymers of greater uniformity and overall quality. Conventional reactor apparatus suffer several disadvantages in this regard. First, the presence of a central shaft through the length of the agitator tends to restrict evaporative flow of volatiles to an exhaust outlet commonly located in the upper region of the discharge end of the vessel and also forms a collection surface on which polymer in adjacent stagnant areas may collect and ultimately become overheated, producing carbonaceous contaminants within the polymeric material. Buildups of the polymeric material can similarly occur at other stagnant regions within the vessel, especially in the end and upper regions of the vessel which may not be satisfactorily wiped by the agitator. The Necessity of mounting the screens to the shaft also limits the closeness at which the screens may be spaced from one another, in turn limiting the evaporative capacity of the vessel. Volumetric capacity of conventional polycondensation vessels is limited by the need to prevent overheating of the polymeric material. A related problem is the inability of conventional reactors to non-invasively measure polymer temperature within the vessel.